Fiber grating sensors, such as Bragg sensors, utilize an optical fiber that transmits light down the length of the fiber. A grating is inscribed in the fiber at periodic locations along the length of the fiber. The grating reflects light of a singular wavelength band and allows all other wavelengths to pass. Thus, the light reflected back to the source is reflected on a narrow optical wavelength band (about 25 nm) when illuminated within a broadband source, such as a super luminescent diode. Alternatively, the light transmitted can be analyzed to observe the narrow optical wavelength bands removed by the grating.
Thermal expansion or contraction of the fiber affects the gratings, which in turn alters the wavelength of the light reflected by the grating. Thus, by sensing the wavelength of the reflected light, a properly configured controller can determine the magnitude of thermal expansion or contraction of the fiber. This magnitude is then used by the controller to extrapolate the temperature of the fiber, as the thermal expansion and contraction rates of the fiber are known.
In this way, a fiber grating sensor can determine the temperature of a component.